The extraordinary increase in agricultural productivity has been a result of many factors, including significantly better understanding of the methods involved with agriculture, improved equipment, availability of fertilizers, and improved pesticides. The latter factor has not been without detrimental aspects, however, due to the negative effect on the environment. There is, therefore, a substantial interest in developing effective and environmentally acceptable pesticides.
Among ecologically acceptable pesticides are the protein toxins produced by various microorganisms, such as Bacillus thuringiensis. However, the use of B. thuringiensis lysate or spores as a pesticide has significant drawbacks. The lifetime of the pesticide is relatively short in the environment, requiring multiple applications to give adequate protection. Consequently, these pesticides are not economical in comparison to more traditional chemical products having long residual activities. Improvements in field longevity would greatly aid in expanding the application of biological, or protein toxin-based pesticides.
As indicated above, there are many requirements for pesticides associated with their particular application. For example, in many cases it is desirable to have pesticides which have long residual activity in the field while not accumulating in the environment. In addition, because of economic considerations, it is preferable to have pesticides which have a reasonably broad spectrum of biocidal activity. Also, the pesticide should degrade to degradation products which are environmentally acceptable. Other considerations include ease of formulation, pesticidal activity, stability to environmental effects, such as light, water, organisms, and the like, and effect on beneficial or innocuous organisms in the environment.
U.S. Pat. No. 4,265,880 describes embedding live insecticidal pathogens in a coacervate microbead. Japanese Pat. No. 51-5047 describes physical-chemical methods for killing B.t. spores, while retaining toxicity.